Kenya and Tanzania have stepped up surveillance in the Maasai Mara Game Reserve following increased poaching.
In the joint operation, wildlife security officers from both counties are conducting a house-to-house search on the common border.
A fortnight ago, three elephants were found dead at Kijirkijirr in Olarro Conservancy on the border.
The Kenya Wildlife Service (KWS) says a suspected poaching mastermind in the Mara escaped a dragnet and fled to Ethiopia.
The man has been linked to Al-Shabaab and is said to be a key financier.
The most recent case was the killing of a black rhino on Sunday.
Identified as Temple, the rhino was marked for easy tracking.
It was found 300 metres from the Kenya-Tanzania border with its horn missing.
Narok KWS Senior Warden Collins Omondi said the animal was killed with a poisoned spear.
Meanwhile, Mr Omondi said samples from seven elephants found dead in the Maasai Mara in the past week have tested negative for anthrax.
He said tests were now being conducted on the possibility of toxic infection.
“We are still waiting for conclusive results but we are glad its is not anthrax. Should it have been an outbreak of the anthrax, other wildlife animals could have been affected,” said Mr Omondi.